This invention relates to linear drives, in general; and, in particular, to a linear drive mechanism employing wave gear technology and an improved oscillating roller assembly to provide motion transfer at non-unity ratio between drive and driven members.
Conventional wave gear drive mechanisms of the type to which the invention relates are illustrated in Rabek U.S. Pat. No. 3,468,175 and Batty U.S. Pat. No. 3,507,159. Such mechanisms produce a non-unity motion transfer between a drive member and a driven member due to cycling, elliptical wave motion induced by a cyclically undulated cam surface on a plurality of oscillators in the form, e.g., of roller elements, placed in between and in simultaneous contact with the cam surface and with an oppositely facing cyclically undulated epicycloidal wave surface or cam track formed by alternating teeth and pocket-shaped recesses. In known arrangements, the number of teeth (or recesses) along a certain length of the cam track is one more or one less than the number of oscillators in an equivalent length along an oscillator carrier. As the cam surface is moved, its cyclic undulations cause each oscillator in turn to be moved in and out of the pockets of the opposing multi-toothed cam track surface, thereby inducing a traveling wave-like reciprocation perpendicular to the cam and cam track surfaces in the series of roller elements. Such reciprocation is used to either drive the member on which the cam track is located or drive an intermediate carrier member on which the roller elements are captured.
In a known rectilinear wave gear motion transmission arrangement, shown in Rabek, a first plate cam member of any desirable length is formed with a periodically or cyclically undulated sinusoidal wave surface having alternating points of maximum and minimum amplitude. A second plate cam member, coplanar with the first plate, has a second cyclically undulated sinusoidal surface of different period to the first surface, located in spaced opposition to the first wave surface across a gap. Mounted between the two cam members is an elongated oscillator carrier member having a plurality of holes formed therein at equal intervals, and oriented laterally of the gap, perpendicular to the undulated surfaces (i.e. oriented perpendicular to lines joining the respective maximum or minimum amplitude points of the first or second undulated surfaces). Oscillators, in the form of elongated members having roller elements located at opposite ends thereof, are respectively slidably received in longitudinal alignment within the holes, one of the roller elements located to bear against the first undulated surface and the other located to simultaneously bear against the second undulated surface. One of the three members (first plate, second plate or carrier) functions as an input or drive member, and either of the remaining members functions as an output or driven member. As the drive member is moved linearly in a direction, the oscillators undergo harmonic reciprocation perpendicular to that direction in response to contact with the facing surfaces, to cause the driven member to be moved in a direction (same or opposite) to the drive direction. The direction of driven movement and the linear velocity transfer ratios being determined by the choice of drive and driven members, the number of teeth, and whether the number of oscillators is one more or one less than the number of teeth.
Rabek also discloses oscillators in the form of elongated roller assemblies oriented perpendicular to the drive/driven directions, as well as to the direction of reciprocation, though not in connection with linear drive mechanisms. A concentric wave gear drive, shown in FIGS. 8 and 9 of Rabek, has oscillating assemblies comprising five laterally spaced, independently rotatable rollers coaxially mounted on common pins which are confined in perpendicular orientation within radially directed channels of an output member rotatable about a common axis with a drive member. The roller element pins are disposed in parallel coincident with the axes of rotation of the drive and driven members. The dimensioning of the rollers is such that the second and fourth rollers ride on identical outwardly-facing cam surfaces axially spaced across a gap, while the central, third rollers ride on an inwardly-facing multi-toothed cam surface oppositely-disposed from the gap. There is no disclosure in Rabek to employ such roller assemblies in the linear drives described by Rabek. There is also no disclosure that the rollers which ride on the dual outwardly-facing undulated surfaces can be of a different diameter than the roller which rides on the inwardly-facing undulated surface; nor that the holes of the carrier be of varying cross-sectional dimension running axially of the assemblies; nor any recognition that wave gear drives can be implemented eliminating some of the oscillators/apertures from the carrier.
Batty, in FIGS. 8-10, shows a linear wave gear drive arrangement wherein oppositely-facing cam surfaces are mechanically coupled by means of carrier-contained oscillators in the form of cylindrical rollers oriented axially perpendicular to the direction of drive or driven motion, and also perpendicular to the direction of reciprocation. The carrier holes are, however, not so oriented. The rollers have reduced diameter ends respectively mounted in opposing slots which are each aligned with the direction of reciprocation. There is no disclosure in Batty of utilizing oscillators having multiple rollers freely independently rotatable about common pin shafts, nor of mounting roller oscillators in carrier holes that are aligned with the pin axes and perpendicular to the direction of the reciprocation. Moreover, neither Rabek nor Batty discloses a linear wave gear drive employed to propel an oscillator carrier linearly down a track having opposing first cam surfaces by drawing a flexible belt having opposing second cam surfaces through the car.